Factors influencing the small-scale distribution of House Sparrows Passer domesticus in a suburban environment

Abstract

Capsule Suburban House Sparrows prefer gardens with native bushes but show no detectable response to garden insecticide use. Aims To identify the factors that influence House Sparrow distribution among suburban gardens. Methods Bicycle transects were used to survey House Sparrows in front gardens in suburban Oxford in the spring of 2004. A subset of 498 gardens was selected comprising all those where sparrows were found and an equal number of randomly selected sparrow-free gardens. In each of these gardens the density of bushes and the proportion of native bushes were recorded and insecticide use and house age were sampled by questionnaire. Binary logistic regression was used to compare these variables with the presence or absence of House Sparrows. A larger scale analysis was also conducted comparing 25 squares, each 250 m2. The density of House Sparrows in the total area of front gardens in these squares was compared to the area of green space within the square, its distance from the city edge and encounter rates of corvids on the cycle transects. Results House Sparrows show a preference for gardens with native bushes. They also prefer gardens with a higher overall density of bushes but appear to make no distinction based on insecticide use or house age. There is no evidence that green space, distance from the city edge or density of corvids affect sparrow numbers at a larger spatial scale. Conclusion House Sparrows might benefit from planting of native bushes but not apparently from a reduction in garden insecticide use. The preference for native vegetation most likely reflects the associated abundance of insect food, which is required by the growing chicks. Further investigation of the habits of House Sparrows in the breeding season may shed light on the causes of the recent decline of the species.